The lymphokine, macrophage migration inhibitory factor (MIF), has been identified as a mediator of the function of macrophages in host defense and its expression correlates with delayed hypersensitivity, immunoregulation, inflammation, and cellular immunity. Although MIF was first characterized as being able to block macrophage migration, MIF also appears to effect macrophage adherence; induce macrophage to express interleukin-1-beta, interleukin-6, and tumor necrosis factor alpha; up-regulate HLA-DR; increase nitric oxide synthase and nitric oxide concentrations; and activate macrophage to kill Leishmania donovani tumor cells and inhibit Mycoplasma avium growth, by a mechanism different from that effected by interferon-gamma.
In addition to its potential role as an immunoevasive molecule, MIF can act as an immunoadjuvant when given with bovine serum albumin or HIV gp120 in incomplete Freunds or liposomes, eliciting antigen induced proliferation comparable to that of complete Freunds. Also, MIF has been described as a glucocorticoid counter regulator and angiogenic factor. As one of the few proteins that is induced and not inhibited by glucocorticoids, it serves to attenuate the immunosuppressive effects of glucocorticoids. As such, it is viewed as a powerful element that regulates the immunosuppressive effects of glucocorticoids. Hence, when its activities/gene expression are overinduced by the administration of excess exogenous glucocorticoids (for example when clinical indicated to suppress inflammation, immunity and the like), there is significant toxicity because MIF itself exacerbates the inflammatory/immune response. See Bucala et al., Ann. Rep. Med. Chem. 33:243-252, 1998.
The interest in developing MIF inhibitors derives from the observation that MIF is known for its cytokine activity concentrating macrophages at sites of infection, and cell-mediated immunity. Moreover, MIF is known as a mediator of macrophage adherence, phagocytosis, and tumoricidal activity. Hence, the inhibition of MIF results in the indirect inhibition of cytokines, growth factors, chemokines, and lymphokines that the macrophage may otherwise bring to a site of inflammation.